result of erf is never more precise than double

3 results were exact to double the precision

20 largest ulp errors (stored in a double)
   0.53615 ulp for erf(0.323079736607112478) = 0.352259768077648028)
   0.52689 ulp for erf(-0.237989233146952112) = -0.263557116890746901)
   0.52554 ulp for erf(0.183825489930280112) = 0.205111928999442333)
   0.52455 ulp for erf(-0.118859142942033036) = -0.133489263867343777)
   0.52414 ulp for erf(0.789433081039224605) = 0.735760585524578681)
   0.52380 ulp for erf(-1.1337890147851819) = -0.891157997841481642)
   0.52372 ulp for erf(-0.237989233146952528) = -0.263557116890747345)
   0.52080 ulp for erf(-1.57543825368511969) = -0.974119894774670647)
   0.51817 ulp for erf(1.45550972655508826) = 0.960448401281772002)
   0.51807 ulp for erf(-0.118859142942033161) = -0.133489263867343916)
   0.51604 ulp for erf(-1.29245567966885266) = -0.932421680527195207)
   0.51470 ulp for erf(-0.11950033357842324) = -0.134202566094570735)
   0.51243 ulp for erf(0.644448162086819432) = 0.637908673562691209)
   0.51150 ulp for erf(1.0962664969880267) = 0.878943654476177727)
   0.51148 ulp for erf(-1.29245567966885422) = -0.932421680527195651)
   0.51022 ulp for erf(-1.62679402298830111) = -0.978587682107815104)
   0.50899 ulp for erf(-0.119500333578423115) = -0.134202566094570597)
   0.50837 ulp for erf(-1.13378901478518546) = -0.891157997841482752)
   0.50750 ulp for erf(1.09626649698801426) = 0.878943654476173508)
   0.50749 ulp for erf(-1.2238890926331345) = -0.916519793341092348)

<tr><td align=left><a href=erf.res>erf</a></td><td align=right>1277</td><td align=right>0.53615</td><td>0.323079736607112478</td><td>0.352259768077648028</td></tr>